1. Field of the Invention
This invention relates to a method of corrosion prevention applied to surfaces of metals for the purpose of preventing corrosion thereof and a corrosion preventive material suitable for use in the method.
2. Description of the Prior Art
Metal products and structures are sometimes used or located under severe environmental conditions or sometimes require a long period of life. These metal products and structures include automobiles, offshore structures, bridges, pipe lines and the like. These metal products and structures have problems of deterioration in the strength and appearance due to corrosion of metals. The prior art has provided various methods of corrosion prevention for the metal products and structures. Painting is one of the most widespread methods and is applied for preventing corrosion in parts of complicated configurations used in automobiles or the like. For example, an automobile door comprises two metal panels, that is, an outer panel and an inner panel. These metal panels are bonded or otherwise, joined together into a hemming structure wherein the outer panel is hemmed or folded back in the vicinity of one end thereof and one end of the inner panel is held in a hemming portion between the outer panel and the folded portion thereof. The hemming portion of the automobile door requires a high level of corrosion resistance. Publication No.6-305329 (1994) of an unexamined Japanese patent application proposes a corrosion proof structure by painting. However, the disclosed structure is insufficient in the effect of corrosion prevention for an adhesive agent, admitting of further improvement in the corrosion proofness.
Another method utilizes sacrificial corrosion prevention and has been put to practical use. For the corrosion prevention of steel products, for example, a corrosion preventive material has been provided wherein a powdered metal which is baser in the galvanic series than iron, such as zinc, is dispersed into a resin. Publication No.2-294370 (1990) of an unexamined Japanese patent application discloses such a corrosion preventive material. As disclosed in the publication, zinc grains whose grain diameters range between 70 to 150 .mu.m are mixed with an adhesive, solvent or filling material in a predetermined mixing ratio. The mixture is brought into contact with a steel product to be protected from corrosion so that zinc is preferentially corroded, thereby preventing corrosion of the steel product.
However, the above-described corrosion preventive material cannot obtain a sufficient effect of corrosion prevention. Furthermore, since the concentration of zinc contained in the material needs to be high, the cost of the material is increased.